1. Field of the Invention
The present invention relates to a semiconductor device in which electric power can be efficiently used by storing the reflected energy generated during signal exchange and recovering the stored energy into power supply voltage.
2. Description of the Related Art
The frequency of signals handled by semiconductors increases every year in conjunction with the current development of digital technologies, and semiconductor devices for transferring data between semiconductor devices have been implemented by using interfaces having frequencies in excess of 1000 MHz. As the frequency of interface signals becomes higher, an increase in the speed of the rise and fall when these signals are driven is required. However, reducing the rise time and fall time of the signals tends to produce overshooting in which the signal waveform temporarily exceeds the stipulated level because of mismatching of the characteristic impedance of the transmission path, and undershooting in which the signal waveform temporarily falls below the stipulated level. Overshooting and undershooting are accompanied by relatively large currents, but are completely unnecessary for signal propagation, and merely increase the power consumption.
The technique disclosed in Japanese Laid-open Patent Application No. 8-149831 is known as a technique that allows the excess voltage energy accompanying the switching operation of a power device to be efficiently recovered on the power supply side. FIG. 1 is a circuit diagram showing the construction of the voltage inverter described in this Japanese Laid-open Patent Application No. 8-149831.
As is shown in FIG. 1, circular-flow diodes 103a and 103b and snubber circuits 104a and 104b are connected in-parallel to GTOs (gate turn-off thyristors) 102a and 102b , respectively. The snubber circuit 104a comprises a diode 114a and a capacitor 115a , and the snubber circuit 104b comprises a diode 114b and a capacitor 115b . Furthermore, a capacitor (energy recovery capacitor) 105 is connected in parallel with the capacitors 115a and 115b via respective diodes 106a and 106b. Moreover, the GTOs 102a and 102b are connected to a direct-current power supply 110 via respective reactors 107a and 107b. 
The steep voltage rise occurring when the GTOs 102a and 102b are off is suppressed by the snubber circuits 104a and 104b; furthermore, the abrupt current variation occurring when the GTOs 102a and 102b are on is suppressed by the reactors 107a and 107b. Moreover, the absorbed energy that charges the respective capacitors 115a and 115b inside the snubber circuits 104a and 104b charges the capacitor 105 via the diodes 106a and 106b in accordance with the switching operation of the GTOs 102a and 102b accompanying the rise in the charging voltage. Furthermore, the capacitor 105 is charged with the absorbed energy of the reactors 107a and 107b via the diodes 106a and 106b when the GTOs 102a and 102b are off.
The voltage inverter 100 is also provided with a voltage comparator circuit 108 for detecting the charging voltage of the capacitor 105; GTOs 111a and 11b, which are switching elements that switch the connection between the capacitor 105 and the direct-current power supply 110 on and off; and ignition circuits 109a and 109b that control this switching operation. When the charging voltage of the capacitor 105 exceeds the power supply voltage, the capacitor 105 and direct-current power supply 110 are connected by switching the switching elements on, and the charged energy of the capacitor 105 is recovered on the power supply side via the reactors 112a and 112b and the diode 113. Furthermore, in FIG. 1, the power supply voltage is used as the comparative voltage of the voltage comparator circuit 108; however, an embodiment that allows comparison with a specified reference voltage is described in Japanese Laid-open Patent Application No. 8-149831.
However, the prior art described in Japanese Laid-open Patent Application No. 8-149831 suffers from the following problems.
In signal transmission via a driver and receiver in a conventional electronic circuit, an increase in the frequency results in an increase in the amount of current that is supplied to the LSI (large scale integrated circuits), so that the consumption of power and generation of heat are increased. Furthermore, such an increase in the amount of heat generated makes it necessary to increase the performance of the cooling system, so that an increase in the size of the heat sink and an increase in the speed of the cooling fan become necessary, resulting in the problem of a deleterious effect on the environment. These problems run counter to the current movement of easing the environmental problems.
As was described above, when the rise time and fall time during the driving of signals in data transfer between semiconductor devices are shortened, overshooting and undershooting, which constitute noise components, are generated as a result of the mismatching of the characteristic impedance of the transmission path, so that the power consumption is increased. Accordingly, if feedback means for reutilizing power arising from overshooting and undershooting can be provided, this will lead to the efficient utilization of power, and the noise component caused by reflection can be reduced.
In the past, energy recovery circuits using snubber circuits have been known, as described in Japanese Laid-open Patent Application No. 8-149831. However, such techniques fail to suppress the overshooting and undershooting generated during high-frequency signal transmission between semiconductor devices, or to reduce power consumption by reutilizing reflected energy.